Various electronic structures must be retained in sealed state or condition within a housing so that the structure is isolated from it's surroundings, and thus isolated from ambient contamination, for example, by atmospheric contamination, humidity, salt spray or the like. A typical application is an electronic control unit enclosed within a housing and installed in a motor vehicle, where changes in ambient humidity, mineral, salt or other contamination of surrounding atmosphere, oil sprays or gasoline vapors, and the like may attack delicate electronic components. The electronic components within the housing may include an adjustable element, such as a potentiometer which must have an externally accessible adjustment part, for example, an adjustment screw, knob, screwhead or the like. Yet, the potentiometer should preferably form part of the sealed structure and preferably be entirely retained within the interior of the housing.
It has been proposed to provide a potentiometer, located on a suitable support which, for example, may be a printed circuit-board (PC board), with an externally projecting adjustment element passing through a bore or opening in the housing. The potentiometer structure, as a unit, or block, must then be fitted precisely within the opening in the housing and tolerances must be compensated-for by flexible seals. Usually, it is possible to deflect the structure or block of which the potentiometer is a part only in a direction perpendicular to the longitudinal axis thereof.
It is quite difficult to mount a PC board with a potentiometer thereon within the housing; particularly, if the potentiometer is a center-type adjustment potentiometer, it may be difficult to introduce the positioning element thereof into the suitable opening of the housing. Unless extreme care is taken, and tolerances are held to a close level, the potentiometer may be damaged upon introduction thereof into the housing. Potentiometers which use coiled wires cannot be adjusted with known adjustment elements since longitudinal tolerances cannot be compensated thereby, but, rather, mechanical pressure may unduly influence the electrical characteristics of the potentiometer. An adjustment device for a coiled-wire potentiometer about which a slider operates has been proposed which adjustment element is held on the inside of the housing by an additional element or part and includes an externally accessible operating or control stud or plug or bolt. The externally accessible and externally adjustable bolt has, at one end thereof, a wave or undulating leaf spring which is releasable secured thereto, the other end of which releasably carries the adjustment screw of the potentiometer. The leaf spring transfers rotary movement between the plug and bolt of the potentiometer. Assembly continues to be complex, however, and the three-part arrangement--potentiometer, leaf spring, adjustment bolt or plug--is a substantial disadvantage. The spacing between the potentiometer and the adjustment bolt or plug must be precisely maintained so that the spring is neither over loaded, nor the potentiometer unduly affected by mechanical loading, thereby, again, impairing the accuracy of adjustment and of the electrical characteristics of the potentiometer.